Fine textile yarns are usually produced on spinning frames, such as ring spinning frames. The technology for preparing fibre material for this production process includes the operation of slubbing, in which a relatively fine cohesive roving is formed from a staple fibre sliver, with a small twist. As it leaves the slubbing frame, the roving is wound on to a roving bobbin to form a feed bobbin for a ring spinning frame. The roving must be a linear textile system with uniform dimensions and mass, and must be suitable for subsequent processing; consequently the protective twist applied to the roving gives it only a low degree of cohesion. When the roving is wound on to the bobbin, a constant tensile force must be maintained on the roving between the point of departure from the slubbing frame and the roving bobbin, without exceeding the rather low tensile strength of the roving imparted by its small twist.
Prior art devices for producing roving include what is known as a flyer spinning frame, which comprises a sliver drafting machine, a flyer, and a spindle. From the drafting machine, the sliver is guided across the guide opening in the fixed plate on the flyer arm, which is fitted rotatably about its vertical axis in the vertically fixed part of the frame. At the lower end of the flyer arm, which retains the sliver, there is a presser finger on to which the sliver is transferred from the inner arm of the flyer, the presser finger being provided with a guide plate adjacent to the surface of the bobbin onto which the roving is wound. The roving is formed by the rotation of the bobbin and the rotation of the flyer. While the roving is being wound onto the bobbin, it passes through a number of turns (wraps) on the surface of the presser finger, which promotes the application of the protective twist, described below, to the roving. The bobbin is positioned with its longitudinal axis vertical, and is fitted on a vertically located rotating spindle which is fitted rotatably on the vertically movable part of the frame. The sliver leaving the drafting frame is twisted into roving by the rotary movement of the bobbin and flyer, and is then wound on to a bobbin in such a way that the flyer with the presser finger rotates around the bobbin, which simultaneously moves vertically to guide the wound roving along the length of the bobbin, the roving receiving a limited twist as a result of the rotary movement of the flyer before the roving is laid on the bobbin. The roving wound in this way has a fibre structure such that each fibre in the cross section of the roving is substantially twisted in the direction of the protective twist of the roving.
A drawback of this equipment is the relatively low roving production rate, averaging 20 to 40 meters per minute, due to the difficulties of the twisting process which make it impossible to achieve high speeds, and therefore high productivity, in the production of roving. A further drawback of this solution is the structure of the resulting roving, in which each fibre in the cross section of the roving is substantially twisted in the direction of the protective twist of the roving, which limits to some extent the attainable quality of yarns subsequently formed from this roving. A further drawback of this arrangement is the relatively high price of such equipment.
There is also a known device disclosed in EP 2 112 258 (US2009/0289141), in which the resulting roving contains fibres lying parallel virtually throughout its cross section and only a few fibres on the outer surface of the roving are wound around the body of the roving, causing the roving to remain sufficiently cohesive and substantially compensating for the protective twist of the roving created on flyer spinning frames. This effect is achieved by using a pneumatic device placed on the sliver drafting frame. The pneumatic device comprises a spinning chamber in which individual fibres of the sliver are wound around the core fibres. After the pneumatic device, there is a roving winder comprising a rotary spindle for a bobbin which is coupled to a driven pair of delivery rollers which are arranged immediately before the roving bobbin, and which have a nip line through which the wound roving passes. In order to guide the roving along the length of the roving bobbin, the delivery rollers can be arranged movably along the roving bobbin or the delivery rollers can be coupled to a guide element which helps to guide the roving along the roving bobbin and along the nip line of the delivery rollers. Similarly, the roving bobbin can be axially movable while the delivery roller remains in place. Since guiding by means of the delivery rollers which are movable along the roving bobbin or by means of a roving bobbin which is movable relative to stationary delivery rollers requires the handling of a relatively large mass, it is preferable to guide the roving by means of a roving guide element when this solution is used. The advantage of this device is that it enables the roving to be wound at high speeds of up to 600 meters per minute, but this solution has the drawback of being technically demanding and occupying a large amount of space, while, owing to the presence of an unguided section between the bobbin and the delivery cylinders, the tension on the roving may be unstable and the roving may break. Another disadvantage is the price.